Scientists from the Hong Kong University of Science and Technology say travelling in time is a wild dream and that nothing can travel faster than the speed of light.

According to the study published in the journal Physical Review Letters, a single photon obeys Einstein’s theory that light is the fastest element.

“The results add to our understanding of how a single photon moves,” explained lead researcher Professor Shengwang Du. “They also confirm the upper bound on how fast information travels with light.”

“By showing that single photons cannot travel faster than the speed of light, our results bring a closure to the debate on the true speed of information carried by a single photon,” he added.

Studies by Du and his team showed that a single photon obeys the traffic law of the universe, mailonline reported.

This is the first research which shows that optical precursors exist at the single-photon level, and that they are the fastest part of the single-photon wave packet in a so-called 'superluminal' - or faster than light - medium.

Professor Du’s team measured the ultimate speed of a single photon with controllable waveforms and came to the conclusion that an effect cannot occur before its cause.